python3: add tk support

Add support to enable tk via PACKAGECONFIG.
before this patch:
 # python3
 Python 3.5.6 (default, Nov  8 2018, 04:53:45)
 [GCC 8.2.0] on linux
 Type "help", "copyright", "credits" or "license" for more information.
 >>> import tkinter
 Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python3.5/tkinter/__init__.py", line 35, in <module>
    import _tkinter # If this fails your Python may not be configured for Tk
 ImportError: No module named '_tkinter'
 >>>

After this patch, if enable tk in PACKAGECONFIG, then
 # python3
 Python 3.5.6 (default, Nov  8 2018, 03:15:52)
 [GCC 8.2.0] on linux
 Type "help", "copyright", "credits" or "license" for more information.
 >>> import tkinter
 >>>

(From OE-Core rev: 4b781d545e7e0b084201cd6a8fad953b0f231513)

Signed-off-by: Mingli Yu <Mingli.Yu@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/python/python3/python3-manifest.json

@@ -1060,6 +1060,7 @@
             "core"
         ],
         "files": [
+            "${libdir}/python${PYTHON_MAJMIN}/lib-dynload/_tkinter.*.so",
             "${libdir}/python${PYTHON_MAJMIN}/tkinter"
         ],
         "cached": []